insert text five lines before each pattern match

Question

I have a file in which a pattern (eg: RotX) is repeated many times in a similar context. I need to insert a specific text (eg: Rot-X) at the start of every line which is located five lines before every pattern match:

...
_face_641
{
 type wall;
 nFaces 6;
 startFace 63948413;
 inGroups 1(RotX);
}
_face_821
{
 type wall;
 nFaces 3;
 startFace 63948419;
 inGroups 1(RotX);
}
_face_67
{
 type wall;
 nFaces 3;
 startFace 63948422;
 inGroups 1(RotX);
}
...

should become

...
Rot-X_face_641
{
 type wall;
 nFaces 6;
 startFace 63948413;
 inGroups 1(RotX);
}
Rot-X_face_821
{
 type wall;
 nFaces 3;
 startFace 63948419;
 inGroups 1(RotX);
}
Rot-X_face_67
{
 type wall;
 nFaces 3;
 startFace 63948422;
 inGroups 1(RotX);
}
... 

Could this be done using sed or awk ?

Many thanks in advance for your help

• Marc: Does the pattern change? For example, could you just preface every line that starts with _ with Rot-X? Or does the pattern within your parentheses vary such that it's not always Rot-X where RotX is found 5 lines later?
• OlM: yes the pattern varies

Answer 1

Using a simple 2-pass approach:

$ awk 'NR==FNR{ if (/RotX/) nrs[NR-5]; next } FNR in nrs{ 0ドル="Rot-X" 0ドル } 1' file file
...
Rot-X_face_641
{
 type wall;
 nFaces 6;
 startFace 63948413;
 inGroups 1(RotX);
}
Rot-X_face_821
{
 type wall;
 nFaces 3;
 startFace 63948419;
 inGroups 1(RotX);
}
Rot-X_face_67
{
 type wall;
 nFaces 3;
 startFace 63948422;
 inGroups 1(RotX);
}
...

• OlM: I tried the 2-pass approach. It works perfectly. Wonderful ! A great thank you to you Ed !

Answer 2

Using vim

vim -c "g/RotX/norm 5kIRot-x" -c "wq" file.txt

Using ed: From @steeldriver

printf '%s\n' 'g/(RotX)/-5s/^/Rot-X/' 'wq' | ed -s file.txt

---

If the braces {, need not be exactly 4 lines above but otherwise same format,

vim -c "g/RotX/norm [{kIRot-X" -c "wq" file.txt
printf "%s\n" 'g/RotX/?^{$?-1s/^/Rot-X/' 'wq' | ed -s file.txt

• steeldriver: ... or similarly using ed, printf '%s\n' 'g/(RotX)/-5s/^/Rot-X/' 'wq' | ed -s file.txt
• balki: @steeldriver cool Thanks!. :) Didn't know ed had the g command

Answer 3

A single pass with awk:

# insert_before_match.awk
{
 p6=p5
 p5=p4
 p4=p3
 p3=p2
 p2=p1
 p1=0ドル
 if (0ドル ~ /RotX/) {
 print "Rot-X"p6
 print p5
 print p4
 print p3
 print p2
 print p1
 print "}"
 print ""
 }
}

$ awk -f insert_before_match.awk infile

Rot-X_face_641
{
 type wall;
 nFaces 6;
 startFace 63948413;
 inGroups 1(RotX);
}
Rot-X_face_821
{
 type wall;
 nFaces 3;
 startFace 63948419;
 inGroups 1(RotX);
}
Rot-X_face_67
{
 type wall;
 nFaces 3;
 startFace 63948422;
 inGroups 1(RotX);
}